Symposium on “Symbiosis in Protozoa”: Introductory Remarks1,2

ABSTRACT. Attention, perhaps overdue, is drawn to the extent and significance of endosymbionts (xenosomes sensu lato) in the cytoplasm and nuclei of many protozoa from diverse taxonomic groups. Even more importantly, recent advances in the study of such intimate associations are reviewed and discussed and their impact on broader problems of cell biology and evolution are stressed. Workers inside and especially outside the fields of protozoology and parasitology have often neglected such data, failing to appreciate their relevance to significant problems in their own fields of investigation. The major topics covered by speakers in the Symposium (to which this paper serves only as an introduction) include the following, in order of their presentation: terminology for the symbiont-host relationship and a brief overview of the field; the evolutionary problem of the origin of contemporary associations, including cell organelles such as mitochondria and plastids; the adaptive value of endosymbionts to their protozoan hosts; mechanisms of establishment, maintenance, and integration of such foreign bodies/invaders in their unicellular eukaryotic host cells; and the extent of algal and bacterial endosymbioses in diverse protozoan groups. In all papers, the principal relatively well studied complexes used as examples are the following: various kinds of algae in the larger foraminifera and in ciliates, radiolarians, and acantharians; the several types of bacteria in the cytoplasm of Amoeba and of Pelomyxa; the endonuclear bacterial symbionts of Paramecium; the cytoplasmic prokaryotes in Paramecium and in Parauronema; and the methanogenic bacteria of certain ciliates.     

Structural Alteration of the Membrane of Erythrocytes Infected with Plasmodium falciparum1

Human erythrocytes infected with five strains of Plasmodium falciparum and Aotus erythrocytes infected with three strains of P. falciparum were studied by thin-section and freeze-fracture electron microscopy. All strains of P. falciparum we studied induced electron-dense conical knobs, measuring 30–40 nm in height and 90–100 nm in diameter on erythrocyte membranes. Freeze-fracture demonstrated that the knobs were distributed over the membrane of both human and Aotus erythrocytes. A distinct difference was seen between the intramembrane particle (IMP) distribution over the knobs of human and Aotus erythrocyte membranes. There was no change in IMP distribution in infected human erythrocyte membranes, but infected Aotus erythrocytes showed an aggregation of IMP over the P face of the knobs with a clear zone at the base. This difference in IMP distribution was related only to the host species and not to parasite strains. Biochemical analysis demonstrated that a higher proportion of band 3 was bound to the cytoskeleton of uninfected Aotus erythrocytes than uninfected human erythrocytes after Triton X-100 extraction. This may account for the different effects of P. falciparum infection on IMP distribution in the two different cell types.     

Calyptospora empristica n. sp. (Eimeriorina: Calyptosporidae) from the Liver of the Starhead Topminnow,Fundulus notti1

Oocysts of Calyptospora empristica n. sp., the second described species in its genus, are described from the freshwater starhead topminnow, Fundulus notti, in southern Mississippi. Oocysts are 22 μm in diameter with a wall about 20 nm thick and have no residuum, micropyle, or polar granule. Sporocysts are spheroid, 9 × 5 μm with a two-layered wall approximately 120 nm thick. They have an oblong apical opening at the anterior pole, a single ornamented sporopodium approximately 5.7 μm long at the posterior pole, and a residuum. An intermediate host, most likely the freshwater grass shrimp Palaemonetes kadiakensis, is probably required to complete the life cycle.     

Habitat preferences of small mammals in tropical open-forest of the Northern Territory

Pattern analysis was used to investigate the habitat preferences of five small mammal species in tropical open-forest of the Northern Territory. Fifty-one sites were classified by faunal abundance and the groups examined for significant differences in vegetation structural attributes and plant species in both dry and wet seasons. The omnivore Isoodon macrourus showed strong association with floristic and vegetation structural attributes only in the dry season, when areas with a dense understorey of small trees and shrubs and a high percentage of leaf litter cover were favoured. Of the two primarily carnivorous species, Antechinus bellus was related strongly with floristic and structural attributes in both seasons and showed a consistent preference for areas with relatively dense low-level foliage (< 2m). By contrast, Dasyurus hallucatus was associated more with the structurally simple open-forest types. Of the two mainly herbivorous species Mesembdomys gouldii showed associations only withfioristics in both seasons, while the habitat relationships of Trichosurus arnhemensis were very weak due to its low abundance in the study area. The number and strength of animal/habitat relationships were greatest in the dry season. Forest types with dense mid-level foliage and abundant hollow logs and leaf litter had the greatest mammal richness and abundance; these areas may be critical to the survival of local mammal populations. A comparison of site-groups, defined independently on the basis of fauna, floristics or structure, showed that animal groups overlapped one to six of the habitat groups. The animal's perception of s‘habitat’ may thus differ from that of humans, or that defined by measurement of habitat attributes.     

Separation of Two Forms of Anthranilate Synthetase from 5-Methyltryptophar Susceptible and -Resistant Cultured Solarium tuberosumCells

Potato cell suspension cultures (Solanum tuberosumL. cv. Merrimack) have been selected which are resistant to growth inhibition by D,L-5-methyltryptophan. Anthranilate synthetase activity in crude extracts from resistant cells was less sensitive to feedback inhibition by L-tryptophan and D,L-5-methyltryptophan than the activity from the sensitive line. This altered feedback control apparently accounts for the cell's resistance to growth inhibition since there is a 48-fold increase in free tryptophan in one of the resistant cell lines. Preparative polyacrylamide gel electro-phoresis separated feedback-sensitive and -resistant forms of anthranilate synthetase in extracts from both 5-methyltryptophan-susceptible and -resistant cells, with a predominance of the corresponding form in the respective cell type. The anthranilate synthetase activity from the 5-methyltryptophan-resistant line was inactivated more slowly by incubation of crude extracts at 50°C than the activity from the sensitive line. These results suggest the presence of two isoenzymes of anthranilate synthetase in cultured potato cells.     

Photosynthetic rates in four tropical African fresh waters

SUMMARY. Seasonal changes in photosynthetic rates of phytoplankton and underwater light in four Kenyan fresh waters (Lake Naivasha, Crescent Island Crater, Oloidien Lake and Winam Gulf) were measured in 1973 and 1974. Daily variations in water temperature were only slightly less than seasonal changes, and complete vertical mixing usually occurred each day. Well oxygenated water from top to bottom provided evidence for daily mixing. The vertical profiles of photosynthetic rates in the four lakes had the familiar feature of subsurface maxima. Of the photosynthetically available radiation (PAR), 1% coincided with the limit of detection of photosynthesis in Naivasha and Crescent Island Crater. The PAR at the depth of the maximal photosynthetic rate was higher for Naivasha (mean= 1.71 einsteins (E) m^?2) than for the Oloidien and Crescent Island Crater (means = 1.23 and 1.20 E m^?2 h^?1, respectively). The maximal rates of photosynthesis (mg O2 m^?3 h^?1) were usually higher in Oloidien (260–750) and Winam Gulf (230–640) than in Naivasha (150–240) and were least in Crescent Island Crater (50–180). Chlorophyll-a concentrations were directly related to photosynthetic rates. Because of the inverse relation between euphotic zone depth and maximal photosynthetic rates, the areal rates varied less among the lakes than the volumetric rates (i.e. 3.0–12.1 g O2 m^?2 day^?1). The efficiency of utilization of PAR expressed on a molar basis ranged from 6.1 to 1.9 mmol O₂ E^?1, but was usually 2–4 mmol O₂ E^?1. The seasonal changes over a 12-month period in the areal photosynthetic rates ranged from a 3-fold variation in Oloidien and Crescent Island Crater to a 1.5-fold variation in Naivasha. In Winam Gulf over a 5-month period a 2.3-fold variation occurred.     

The relation between body size and resistance to desiccation in two species of Zaprionus (Drosophilidae)

Abstract.

• 1 Resistance to desiccation and body size were studied in the drosophilid flies Zaprionus vittiger and Z.tuberculatus.
• 2 Populations in a hot dry low altitude area were compared with those in a nearby cooler wetter high altitude area in the north-eastern Transvaal of South Africa, using laboratory strains established from these populations.
• 3 No between-area differences were found for either body size or resistance to desiccation considered separately.
• 4 However, in Z.tuberculatus, regression analyses using strain mean values showed a strong positive correlation between the two characters amongst strains derived from low altitude populations but not amongst strains derived from high altitude populations.
• 5 It is concluded that differences of genetic organization have evolved between low and high altitude populations of Z.tuberculutus.
• 6 From differences between species and sexes it is concluded that both body size and some unknown factor related to sex may influence resistance of desiccation.

     

Hammondia pardalis sp. n. (Sarcocystidae) from the Ocelot, Felis pardalis, and Experimental Infection of Other Felines

Synopsis.
Hammondia pardals sp. n. (Eimeriorina: Sarcocystidae) from Panama Canal Zone is described as an obligate heteroxenous coccidian, with felids as the final host and laboratory mice as the experimental intermediate host. Ovoid oocysts. measuring 40.8 (36–46) × 28.5 (25–35) m. are shed unsporulated. Oocysts were infective only for the intermediate host. the laboratory mouse, Mus musculus , and the intracellular cysts were infective only for felids. Attempted passage of tissue cysts from mouse to mouse was unsuccessful.
Mice fed 5 × 10⁴ sporulated oocysts were found to harbor small intracellular cysts, 13–16 × 10–15 m, in the mesenteric lymph nodes, lungs, and intestinal submucosa 15 days postinfection. The meronts in these early cysts were stubby and measured 3 × 6 m. The prepatent period in the felids was 5 to 8 days and the patent period 5–13 days. Experimental infections of definitive hosts were successful with 6/6 domestic laboratory-reared kittens, Felis catus ; 5/5 ocelots, F. pardalis ; and 1/1 jaguarundi, F. yagouaroundi. None of the exposed raccoons, Procyon lotor , shed oocysts.     

Evolution and Ecology of Parthenogenesis in Earthworms

A model for the origin of parthenogenesis in hermaphroditesis developed. If a dominant mutation causing parthenogeneticdevelopment of eggs without affecting meiotic production ofsperm arises, the parthenogens will increase in frequency tofixation. Concomitantly, there is selection for reallocationof resources from male to female-related functions in both parthenogeneticand sexual individuals. Occasional fertilization of unreducedeggs may produce polyploid clones. Both the loss of male-relatedstructures and polyploidy are common in parthenogenetic earthworms.Parthenogenesis should be favored in patchy and temporally unstablehabitats, in which -selection may be expected, because it facilitatescolonization and rapid population growth, and because selectionby the biotic component of the environment presumably is reduced.Parthenogenetic earthworms commonly occur in decaying logs,leaf litter, and the upper, organic layers of the soil, whereassexual species more often inhabit the deeper, more stable soilhorizons. Long-term persistence of clones depends on their abilityto survive and reproduce under a variety of environmental conditions.It is proposed that successful clones possess "general purpose"genotypes that allow persistence in spite of temporal changesand facilitate active dispersal through heterogeneous environmentsbetween patches of prime habitat. Two common clones of the parthenogeneticearthworm Octolasion tyrtaeum seem to possess general purposegenotypes, as they occur in a wide variety of soil and habitattypes and are geographically widespread.     

Evolution of the tetrapod ear: an analysis and reinterpretation

The dominant view of tetrapod otic evolution–the “standard view”–holds that the tympanum developed very early in tetrapod history and is homologous in all tetrapods and that the opercular process of the rhipidistian hyomandibula is homologous to the tympanic process of the stapes in lower tetrapods. Under that view, the labyrinthodont amphibians of the Paleozoic are usually considered ancestral to reptiles, and thus the “otic notch” of labyrinthodonts and the tympanum it presumably contained form the starting-point for middle ear evolution in reptiles. Four problems have classically been identified with the standard view: the differing relationships of the internal mandibular branch of N. VII (chorda tympani) to the processes of the stapes in amniotes and anurans; the differing orientations of the stapes in key fossil and living groups; the location of the tympanum in early fossil reptiles; and the transferral of the tympanum, during the origin of mammals, from the stapes to the articular bone of the lower jaw. An examination of these problems and of the solutions proposed under the standard view reveals the ad hoc, and therefore unsatisfactory, nature of the proposed solutions. To organize and review alternative hypotheses of otic evolution an analytical table is constructed, using three characters (tympanic process, Nerve VII, tympanum), each with two possible states. A total of eight hypotheses about middle ear evolution are possible under this system, one of which is the standard view. The seven “non-standard” hypotheses, only five of which have been argued in the literature, are briefly examined. Six of the “non-standard” hypotheses appear unattractive for various reasons, including reliance on ad hoc arguments. The seventh was first proposed by Gaupp in 1898. It is today almost universally ignored but apparently largely for historical rather than scientific reasons. This hypothesis, her called the “alternative view”, appears to rest on assumptions equally as plausible as those of the standard view. Moreover, it offers a solution of the problems associated with the standard view without, apparently, raising any similarly serious problems. This paper compares the standard and alternative views of middle ear evolution in detail. Comparison proceeds on two levels. On one level, they are compared in terms of the hypotheses of phyletic tetrapod relationships each promotes and how strongly each supports its hypothesis. Both views promote the same hypothesis of tetrapod relationships. The alternative view is the more parsimonious, but the difference is not considered sufficient to provide a choice. On another level, the two views are compared in terms of their implications for: (1) the evolution of relative and absolute auditory perceptive ability; (2) the origin of reptiles; (3) the evolution of the suspensorium and cranial kinesis; and (4) the origin and evolution of recent amphibians. The nature of the data required for a test of the implications of the two views is specified in each case. Where data are available. the alternative view is consistent and the standard view is inconsistent with these data. We conclude that the alternative view is the preferable hypothesis of middle-ear evolution. This conclusion implies the following: the tympanic membranes and the tympanic processes of the stapes in recent mammals, reptiles + birds. and frogs. are not homologous; the evolution of “special periotic systems” in the ancestors of amphibians and amniotes were independent events and preceded the evolution of tympanic membranes; the amphibian tympanic membrane. probably including that of labyrinthodonts. is not ancestral to that of amniotes. and that labyiinthodonts with an otic notch are not suitable as amniote ancestors; the stapes of early reptiles functioned primarily as part of the jaw suspension rather than in hearing; the mechanisms and abilities of sound perception in recent tetrapods are likely to be diverse rather than forming parts of a cline; and the lack of a tympanum in Gymnophiona and Caudata may be a retention of a primitive condition.